Parallel point to plane electrostatic precipitator particle size sampler

ABSTRACT

An electrostatic precipitator is provided for precipitating particulate matter within a fluid onto a grid. An elongated electrode with a sharpened point is positioned with its long axis in spaced-apart relationship parallel to the grid with the grid and electrode in a chamber of a housing. A high voltage is imposed between the grid and the electrode sufficient to cause a corona discharge from the electrode which will precipitate the particulate matter from the fluid onto the grid.

United States Patent 11 1 Sehmel 1 51 Apr. 29, 1975 1 PARALLEL POINT T0PLANE ELECTROSTATIC PRECIPITATOR PARTICLE SIZE SAMPLER [75] Inventor:George A. Sehmel, Richland, Wash.

[21] Appl. No.: 403,751

[52] US. Cl. 73/28; 55/270; 55/152;

55/154; 73/4215 R; 73/421.5 A [51 Int. Cl. B03c 3/04 [58] Field ofSearch 55/152, 154, 128, 129,

55/138. 146. 270; 73/23, 28, 421 R, 421 B. 421.5 R, 421.5 A, 422 R;324/32, 71 R, 71 CP 2,538,562 1/1951 Gustin ct a1. 118/622 X 3.1812855/1965 Tcpolt ct 11.. 55/138 3,320,151 5/1967 Tcpe et 55/138 X 3,434,4163/1969 Testone 101/416 3.478.494 11/1969 Lustcnader et 210/512 X3,561,253 2/1971 Dorman 1 3l0/8.1 X 3.701.236 10/1972 Rotsky ct a155/114 3,718.029 2/1973 Gourdine ct 324/71 PC X Primary Examiner-BernardNozick Attorney Agent, or Firm-John A. Horan; Arthur A. Churm; Paul A.Gottlieb [57] ABSTRACT An electrostatic precipitator is provided forprecipitating particulate matter within a fluid onto a grid An elongatedelectrode with a sharpened point is positioned with its long axis inspaced-apart relationship parallel to the grid with the grid andelectrode in a chamber of a housing. A high voltage is imposed betweenthe grid and the electrode sufficient to cause a [56] References Citedcorona discharge from the electrode which will pre- UNITED STATESPATENTS cipitate the particulate matter from the fluid onto the 1.4256378/1922 Eschholz 55/152 x grid 1,995,790 3/1935 Anderson 55/154 X2,097,233 10/1937 Mcston 55/154 X 4 Claims, 5 Drawing Figures H/Gl/ 28VOL7flGE suPPLy 'r' I I V wiry/$.31 I151 ,40

- =2- '1 i\\\T\\\\"\\\\\\\\ I I8 /7 PARALLEL POINT TO PLANEELECTROSTATIC PRECIPITATOR PARTICLE SIZE SAMPLER CONTRACTUAL ORIGIN OFTHE INVENTION The invention described herein was made in the course of,or under a contract with the UNITED STATES ATOMIC ENERGY COMMISSION.

BACKGROUND OF THE INVENTION Electrostatic precipitation is a method ofremoving particles from fluids by charging the particles to one polarityand then attracting and collecting the charged particles on an electrodeof opposite polarity to the charged particles. One application of thistechnique is a point to plane precipitator which may be used inconjunction with electron microscope studies of particulate matter. Theparticulate matter is deposited on a grid electrode which is mountablein an electron microscope for examination of properties such as particlesize distribution.

The prior art device, herein referred to as the perpendicular point toplane electrostatic precipitator, requires a high-voltage elongated wireelectrode whose end is sharpened to a point. The sharpened end ispositioned directly opposite and perpendicular to a grid, which ismountable on an electron microscope. By applying a sufficient voltagebetween the grid and the pointed end of the electrode a corona dischargefrom the electrode is produced which will charge particulate mattercoming in contact with the corona discharge. These charged particles arethen attracted by the grid because of the difference in potentialbetween the particles as charged by the wire electrode and the grid.

In order to hold the electrode perpendicular to the grid and to supplythe necessary high voltage to the electrode, the dimensions of theprecipitator, particularly parallel to the long axis of the electrode,are relatively large and cumbersome for many applications. As fluidaccess to the electrode and grid is perpendicular to the long axis ofthe electrode, application of the perpendicular point to planeprecipitation geometry is not feasible where the area of access to thefluid is limited. For example, to sample particulate matter in the fluidin a smoke stack, a rather large hole would have to be drilled in thestack wall to allow the electrode and grid to be positioned adjacent tofluid flow in the stack for sampling. Similarly where the desiredmounting is within a pipe the perpendicular point to plane orientationis impractical.

Distortion of sampling results may occur in tests such as particle-sizesampling due to premature particle separation prior to the precipitationof the particulate matter onto the grid. In the perpendicular point toplane design premature separation may result from the manner in whichthe fluid to be tested is provided with access to the electrode andgrid. It is common practice in the perpendicular point to plane designto provide access with an inlet tube or other device interposed be tweenthe fluid to be sampled and the electrode and grid. Due to interactionof the particulate matter with the inlet tube walls, the inlet tube maycause premature particle separation. Even with no separate inlet tubeand access of the fluid provided by an opening in the precipitatorextending to the electrode and grid, in order to insulate properly theperpendicular electrode from energy losses, where the voltage levels ofthe electrode may be 7000 volts or more, the length of the opening maybe large enough so that the precipitator structure itself causespremature separation.

It is therefore an object of this invention to provide an improvedelectrostatic precipitator.

Another object of this invention is to provide an electrostaticprecipitator having minimal premature particle separation.

SUMMARY OF THE INVENTION Precipitation of particulate matter in a fluidonto a grid is achieved with a parallel point to plane design. Anelongated wire electrode with one end sharpened to a point is positionedin spaced-apart relationship from and parallel to a grid. Both the gridand electrode are supported by a housing and are located within achamber in the housing. A voltage is applied between the electrode andthe grid sufficient to cause a corona discharge from the sharpened endof the electrode. An opening is provided in the mounting member to allowfluid access to the grid and electrode. The distance from the electrodeand grid to the beginning of the opening is minimized to retardpremature particle separation. The device may be operated in a directedfluid stream by positioning the electrode with its long axis parallel toand its sharpened point directed against the direction of flow, or thedevice may be operated by positioning the opening in contact with astatic fluid sup- BRIEF DESCRIPTION or THE DRAWING FIG. 1 is a sectionalview of the precipitator;

FIG. 2 is a sectional view along line 2-2 of FIG. 1;

FIG. 3 is a sectional view along line 3-3 of FIG. 1;

FIG. 4 is a view of the precipitator incorporated into a conduit system;and

FIG. 5 is a view of the precipitator installed in the wall of an exhauststack.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, FIG. 2 andFIG. 3, there is shown a parallel point to plane electrostaticprecipitator. The main functional elements of the precipitator aresupported by housing 10 which includes individual mounting pieces 11 and12, which are held together by set screw 13. Mounting pieces 11 and 12should be constructed of an insulating material.

In this embodiment, mounting piece 1 1 is designed to provide a mountingfor the grid assembly. The grid assembly includes pedestal 16 upon whichgrid 17 is mounted. Grid 17 is constructed of wire mesh formed into aflattened pancake providing a flat conductive surface and may be astandard electron microscope specimen holder suitable for removal andmounting on an electron microscope for examination of the collectedspecimen. Grid 17 is secured to pedestal 16 by grid cap 18. Best resultsmay be obtained if grid cap 18 is made of a nonconducting material or iscoated with a nonconducting material to avoid collection of particles onthe cap during precipitation. Pedestal 16 is screw threaded and screwedinto threaded grid mounting hole 19 of mounting piece 11. As pedestal 16is screwed into hole 19, grid 17 and grid cap 18 will eventuallyprotrude into chamber 20. Grid 17 is connected to wire 21 which extendsthrough the body of housing 10.

Mounting piece 12 provides mounting for the wire electrode 24. Electrode24 is positioned in mounting hole 25 of mounting piece 12 and maintainedthere by set screw 26 engaging the insulator 23 of electrode 24. One endof the elongated wire electrode 24 is formed into a sharpened point 27.By means of mounting piece 12, the elongated wire electrode 24 ispositioned with its long axis parallel to the diameter of the flattenedpancake shape of grid 17 and its sharpened end 27 is generallypositioned over grid 17 so that a corona discharge may be developedbetween end 27 and grid 17.

Electrode 24 and wire 21 are coupled to a highvoltage supply 28. With asufficient voltage provided between electrode 24 and grid 17, a coronadischarge without arcing will occur between sharpened end 27 and grid17. Varying the separation between sharpened end 27 and grid 17 withscrew pedestal 16 will vary the voltage difference necessary to cause acorona discharge so that the greater the separation the greater thevoltage required. At a particular separation between grid 17 andsharpened end 27 an increase in voltage above the minimum voltagenecessary to cause corona discharge will produce an increase in theassociated corona current therebetween. With a 0.039 inch diametertungsten wire as elongated wire electrode 24 and with end 27 sharpenedto a point of 20 micrometers in diameter, corona currents of tomicroamperes were obtained for voltages of 4,000 to 6,000 volts. At5,000 volts corona currents between 1 and 10 microamperes were obtainedby varying the separation between sharpened end 27 and grid 17 from0.235 inch to 0.181 inch.

When a fluid is introduced into chamber in the presence of a coronadischarge from sharpened end 27, particulate matter in the fluid willbecome charged to the polarity of the corona by interaction with thecorona discharge and be attracted to grid 17 because of the differencein polarity between grid 17 and the charged particles. Chamber 20 is ahollowed-out portion of housing 10 encompassing grid 17 and electrode 24and access for fluid to grid 17 and electrode 24 is provided throughopening 29 in housing 10. If separation A, which is the distance betweensharpened end 27 and the beginning of opening 29 adjacent the fluid, isincreased with respect to separation B, which is the narrowestcross-sectional dimension of opening 29 over the length of separation A,or if separation B is decreased with respect to separation A, prematureparticle separation may result due to the interaction of particulatematter within the fluid with the body of housing 10 prior to contact ofthe particulate matter with the corona. It has been observed that theratio of separation A to separation B should not be greater than 2 to 3to limit the possibility of premature separation caused by housing 10.An example of appropriate dimensions found to limit premature separationis .2 inch for separation A and .3 inch for separation B.

There are several methods of introducing fluid into chamber 20 and ofpositioning housing 10 relative to a volume of fluid so that fluid willenter chamber 20. In one embodiment, fluid enters chamber 20 throughopening 29 in the direction of arrow 30 with sharpened end 27 directedagainst the flow so that premature separation which might be caused bythe interaction of the body of electrode 24 with fluid particles islimited. The fluid exhausts chamber 20 through passageway 31. Bestresults are obtained if passageway 31 is positioned below the center ofchamber 20 and below grid 17 so that the fluid flow will be broughtcloser to grid 17, im-

proving the efficiency of particle deposition on grid 17.

When the fluid is flowing through a pipe system, as shown in FIG. 4,housing 10 may be incorporated within the pipe system between pipes 32and 33 and fastened by set screws (not shown), with the direction offluid flow as indicated by arrow 36 toward sharpened end 27 andcontinuing through passageway 31. Note that the limited diameter of theparallel point to plane design perpendicular to the direction of flowworks a great saving of space, not requiring as much diametric space aswould be the case with a perpendicular point to plane design and thatthe limited separation A will not unduly obstruct the flow to causepremature separation upstream from grid 17. A pump 37 may be provided todraw fluid through housing 10.

In other applications it may be desirable to expose the precipitatordirectly to the fluid. For example, in sampling particles in the air ina room the precipitator, as shown in FIG. 1, can be placed on a tableand the fluid drawn through chamber 30 by a pump 40 coupled to housing10 by pipe 41 and set screw 42. Here again the narrow separation Alimits premature separation which might be caused by an inlet tube andallows accurate size sampling. This method of sampling is also welladapted to exhaust stack sampling, as shown in FIG. 5. All that isrequired is that a hole conforming to the size of housing 10 be drilledin the wall 45 of a stack and the precipitator is then inserted into thehold with opening 29 beginning at the interior side 46 of wall 45 andpassageway 31 exhausting at exterior side 47 of wall 45. This type of insitu stack sampling yields a truer picture of particle characteristicsin a stack than top of the stack samplers. This would be difficult usingthe prior art perpendicular point to plane precipitator because of thesize of the hole required for insertion.

What is claimed is:

1. An electrostatic precipitator for precipitating particulate matterfrom a volume of fluid, comprising: a housing having a chamber thereinwith an opening connecting said chamber with the volume of fluid so thatsaid volume of fluid has free access to said chamber, a passagewayconnected to said chamber of said housing extending from said chamber toa point without said housing so that fluid entering said chamber throughsaid opening exhausts said chamber through said passageway, a flatconductive collector electrode surface being supported by and separatefrom said housing and being positioned within said chamber, an elongatedelectrode axially of the chamber having a point at one end and a longaxis passing through said point, said elongated electrode beingsupported by said housing and being positioned within said chamber inspacedapart relationship with said flat conductive surface and with saidlong axis parallel thereto, said point being abreast of said flatconductive surface and directed toward said opening with the distancebetween said point and said volume of fluid through said opening beingless than or equal to two-thirds of the narrowest crosssectionaldimension of said opening, and voltage supply means coupled to saidelectrode and said surface to provide a voltage sufficient to cause acorona discharge therebetween, whereby particulate matter in the fluidcontacting said corona discharge is precipitated onto said surface.

2. The electrostatic precipitator of claim 1 further including pumpmeans coupled to said passageway, said pump means being able to drawfluid from said volume into said second conduit.

4. The electrostatic precipitator of claim 2 wherein said housing isinstalled in the wall of an exhaust stack having fluid therein with saidopening providing access for said fluid within said stack to saidchamber and with said passageway extending from said chamber to theexterior wall of said stack.

1. An electrostatic precipitator for precipitating particulate matterfrom a volume of fluid, comprising: a housing having a chamber thereinwith an opening connecting said chamber with the volume of fluid so thatsaid volume of fluid has free access to said chamber, a passagewayconnected to said chamber of said housing extending from said chamber toa point without said housing so that fluid entering said chamber throughsaid opening exhausts said chamber through said passageway, a flatconductive collector electrode surface being supported by and separatefrom said housing and being positioned within said chamber, an elongatedelectrode axially of the chamber having a point at one end and a longaxis passing through said point, said elongated electrode beingsupported by said housing and being positioned within said chamber inspaced-apart relationship with said flat conductive surface and withsaid long axis parallel thereto, said point being abreast of said flatconductive surface and directed toward said opening with the distancebetween said point and said volume of fluid through said opening beingless than or equal to two-thirds of the narrowest cross-sectionaldimension of said opening, and voltage supply means coupled to saidelectrode and said surface to provide a voltage sufficient to cause acorona discharge therebetween, whereby particulate matter in the fluidcontacting said corona discharge is precipitated onto said surface. 2.The electrostatic precipitator of claim 1 further including pump meanscoupled to said passageway, said pump means being able to draw fluidfrom said volume of fluid through said opening into said chamber andthrough said passageway.
 3. The electrostatic precipitator of claim 2further including first and second conduits with said fluid beingconfined in said conduits, said housing being coupled to said conduitsso that due to drawing of said fluid by said pump means said fluidpasses into said opening from said first conduit and passes out saidpassageway into said second conduit.
 4. The electrostatic precipitatorof claim 2 wherein said housing is installed in the wall of an exhauststack having fluid therein with said opening providing access for saidfluid within said stack to said chamber and with said passagewayextending from said chamber to the exterioR wall of said stack.